Bruce Jenner Is Obsessed with a Youthful Look: Source

Bruce Jenner appears to be going through a transformation – at least on the outside.

The former Olympian and Keeping Up with the Kardashians star, 64, stepped out with ombré highlights to his longer 'do Monday, following reports that he underwent surgery to decrease the size of his adam's apple – a cosmetic procedure known as a laryngeal shave.

There's been a flood of speculation about the motivation behind Jenner's changing appearance, but insiders tell PEOPLE that his new found freedom and a desire to stay youthful are the origin of his new look.

"He totally has this 'I may be an old man, but I'm cool and young too' syndrome and no one can tell him otherwise," says a close source.

After ending his 22-year marriage with Kris Jenner last fall, "he's a bit lonely, but he's doing his thing," says a family source. "Everything in the end of his marriage just became too much for him and his freedom is really liberating. He wanted to grow his hair long, so he did it. He wants to get manicures, so he gets them," adds the source.

Having moved out of the Calabasas home he shared with Kris, 58, and their two daughters, Kendall, 18 and Kylie, 16, not to mention their frequent visitors – step-daughter Kim Kardashian, 33, her daughter North West and fiancé, Kanye West, 36 – Bruce is now living alone in Malibu but closer to his two sons Brody, 30, and Brandon, 32.

"People in the family have brought up his hair or his clothes, whatever it is and how absurd they think it is, but Bruce doesn't care, nor does he want to listen to any kind of criticism," says the close source.

"He thinks he looks great and cool and that's that. But at the end of the day, however ridiculous people may think he looks, he's happy about it – or at least trying to find what he's happy with – so you really can't blame the guy for that."

In November, Bruce was candid about the criticism the family gets telling PEOPLE, "Sometimes they'll take some really, really tough shots at the family when they're not deserved and totally false, especially with my kids.

"I don't care what they say about me, but when they start ragging on my kids for things that they're not doing and totally misrepresenting them, that really, really bothers me to say the least."

As for all the recent criticism the former Olympian himself is now getting for his changing look, "He's doing what he wants to do," says the source. "It's just a matter of choice and not everybody has the same taste."